I just completed two big projects.
First one is my massive piston theater that is 25 units high and 156 units long on the track. If you saw the digital diamond piston theater at 1.7's release, you understand how this works (for the most part anyway, I had to come up with a somewhat complicated system of bringing back blocks to rid of the audience viewing any pistons). Here it is from the audience's view, and then two views of the wiring behind it:
And then I just completed a huge desert fortress city in a Primordial Desert map. This picture is a little outdated, since the blank spot to the left is now filled with a farm, but am waiting on OptiFine to be updated before getting new pictures and posting a thread on the forums (it really only looks good with dokucraft, or a variation of). It features a minecart station with 22 platforms with piston minecart reset, a library, fallout shelter, residential buildings, shopping district, etc. It is 175 x 175 units.